The work takes scientists closer to making other complex solid organs such as livers using a patient's own cells, the researchers reported in the Proceedings of the National Academy of Sciences on Monday.

It provides a tailor-made transplant, said Dr. Anthony Atala of Wake Forest University Baptist Medical Center's Institute for Regenerative Medicine, who led the study.

"Once the tissue is there, the body recognizes the tissue as its own," Atala told Reuters in a telephone interview.

Atala focused on the penis because he is a pediatric urologist, who has specialized for years in disorders and congenital defects of the bladder and sexual organs. "One of the major challenges that we find is babies who are born with inadequate organs, and right now there are not a lot of options" he told msnbc.com.

In addition to his background in urology, Atala is a specialist in regenerative medicine, which uses the body's own cells to repair damage. In this case, Atala's team used ordinary rabbit cells, not the stem cells often used in such research.

Atala's team first created a scaffold using the penis of a rabbit, and removed all the living cells from it, leaving only cartilage. They then took a small piece of tissue from the penis of another rabbit and grew the cells in a lab dish.

Atala said the work has taken his team 18 years to complete. "We had to find the right growth factors, the right soup to grow the cells in," he said.

They made sure to have two cell types, smooth muscle cells and endothelial cells, the same type of cells that line blood vessels. The smooth muscle cells made the organ's spongy tissue and the endothelial cells grew into blood vessels — very important in an organ like the penis, which requires good blood supply.

The cells were seeded onto the scaffold, and six weeks later the researchers had penises to graft onto rabbits that had their penises removed.

The animals seemed to realize they had working organs again — the 12 with the grafts tried to mate with female rabbits within one minute of being put into cages with them, and four of the female rabbits became pregnant.

Those with the scaffolding alone and no working tissue did not even try.

Atala is hoping the procedure will work with people, perhaps starting with adult men who have had damage to their organs. "Patients with congenital anomalies, penile cancer, traumatic penile injury, and some types of organic erectile dysfunction could benefit from this technology in the future," the team wrote in the report.

The process takes six weeks from beginning to end, he said, and there is reason to believe a penis grafted onto a baby would grow with the child. That turned out to be the case with the rabbit experiment.

"The body recognizes this as its own organ," Atala said.

Atala hopes the approach will work with other organs. "We have made clitoral tissue in the past," he said. "We have extensive work going on with kidneys and livers."

Atala's team started their experiments with replacement bladders grown from patients' cells. Patients fitted with artificial bladders have been enjoying good function for 10 years now, Atala said.

Atala declined to say how long it would be before the procedure is applied to human patients. "We always think it's going to happen sooner than it does," he said.